Is it possible to define literary genres by public consensus?
Iraq bans Blackwater? US State Dept turtle to operate without its shell?

"alternate universes have to be good for something"

Network Stephen Wolfram has written a few thousand words on the structure of universes which is, as might be expected, quite interesting. My favorite passage is this one:

A good friend of mine has kept on encouraging me not to throw away any even vaguely plausible universes--even if we can show that they're not our universe. He thinks that alternate universes have to be good for something.

I certainly think it'll be an interesting--almost metaphysical--moment if we finally have a simple rule which we can tell is our universe. And we'll be able to know that our particular universe is number such-and-such in the enumeration of all possible universes.

As a science fiction editor, I know what alternate universes are good for!